The overall objective of this study is to determine the mechanism by which calcium causes human red cell membranes to lose deformability, and contract. The immediate focus of the research is on the interaction of two proteins, spectrin and actin, with each other and with lipid bilayers. These two proteins are associated in a "fibrillar" layer juxtaposed to the inner surface of the lipid bilayer. Changes in spectrim's enzymatic activity (ATPase) on addition of actin or lipid, or both, will be determined. In parallel, electron microscopy will be used to observe changes in structure of spectrin and actin fibrils, and to observe binding to liposomes. Spin labelling will be used to observe changes in conformation of spectrin and actin on interaction with each other and lipid. In later stages of the project, proteins potentially involved in regulation of contractility will be isolated from erythrocytes and muscle and added to the system. In addition, alteration in the properties of the contractile system during aging of the erythrocyte, both in vivo and in vitro will be studied and studies on spectrin and actin from abnormal cells will also be made, in particular on hereditary spherocytes and on irreversible sickled cells from sickle cell anemia. Towards the end of the project, systems analogous to that in the red cell will be looked for in other cell types, such as white cells, since it now appears likely that membrane-associated contractile systems are present in all mammalian cells with the erythrocyte presenting a simplified (and possibly specialized) system which is easily amenable to study.